Regulatory inhibition of biological tissue mineralization by calcium phosphate through post-nucleation shielding by Fetuin-A

TL;DR

This paper models how proteins like Fetuin-A regulate calcium phosphate mineralization in tissues, preventing unwanted calcification despite high ion concentrations, using a mathematical approach based on classical nucleation theory.

Contribution

It introduces a mathematical model for post-nucleation surface-shielding by proteins, providing insights into biological regulation of tissue mineralization.

Findings

Identifies critical protein concentration for mineralization inhibition

Develops a system of PDEs describing mineral sedimentation regulation

Highlights conditions preventing ectopic calcification

Abstract

In vertebrates, insufficient availability of calcium and phosphate ions in extracellular fluids leads to loss of bone density and neuronal hyper-excitability. To counteract this problem, calcium ions are present at high concentrations throughout body fluids -- at concentrations exceeding the saturation point. This condition leads to the opposite situation where unwanted mineral sedimentation may occur. Remarkably, ectopic or out-of-place sedimentation into soft tissues is rare, in spite of the thermodynamic driving factors. This fortunate fact is due to the presence of auto-regulatory proteins that are found in abundance in bodily fluids. Yet, many important inflammatory disorders such as atherosclerosis and osteoarthritis are associated with this undesired calcification. Hence, it is important to gain an understanding of the regulatory process and the conditions under which it can go awry. In this manuscript, we adapt mean-field classical nucleation theory to the case of surface-shielding in order to study the regulation of sedimentation of calcium phosphate salts in biological tissues through the mechanism of post-nuclear shielding of nascent mineral particles by binding proteins. We develop a mathematical description of this phenomenon using a countable system of hyperbolic partial differential equations. A critical concentration of regulatory protein is identified as a function of the physical parameters that describe the system.